Ecosystems and the Environment: notes

Key Terms

• Ecosystem: All the living things (biotic) and non-living things (abiotic) in an area, and how they interact.
• Habitat: The place where an organism lives.
• Population: All the individuals of one species in one area.
• Community: All the different populations living together in one area.

Food Chains, Webs and Pyramids

• Food chain: A simple path showing who eats whom, e.g. grass → grasshopper → frog → snake. Arrows point in the direction energy flows.
• Food web: Many food chains linked together in one ecosystem.
• Producer: Green plants that make their own food by photosynthesis.
• Pyramid of numbers: A diagram showing how many organisms are at each trophic level. Producers are usually at the base.

Energy Flow and Nutrient Cycles

• Energy flow: Energy enters the ecosystem as sunlight and passes along food chains. Only about 10% is passed on at each step; the rest is lost as heat.
• Carbon cycle: Carbon moves from air (CO₂) to plants by photosynthesis, to animals by feeding, and back to air by respiration and burning.
• Nitrogen cycle: Nitrogen-fixing bacteria change nitrogen gas into nitrates that plants can use.
• Water cycle: Water evaporates, condenses, falls as rain, and flows back to the sea.
• Decomposer: Bacteria and fungi that break down dead matter and return nutrients to the soil.

Human Impact on the Environment

• Deforestation: Cutting down trees, which leads to loss of habitats and soil erosion.
• Soil erosion: Loss of topsoil by wind or water, often after vegetation is removed.
• Pollution: Harmful substances added to air, water or land, e.g. smoke, sewage or waste.
• Global warming: A rise in Earth's average temperature, caused mainly by greenhouse gases such as CO₂ trapping heat in the atmosphere.

Conservation and Sustainable Use

• Conservation: Protecting wildlife and natural resources from being lost or destroyed.
• Sustainable use: Using resources in a way that they can be replaced or renewed for future generations.

Worked Calculation: Energy Transfer

If producers store 10 000 kJ of energy, the energy passed to primary consumers is: 10 000 × 10% = 1 000 kJ The energy passed to secondary consumers is: 1 000 × 10% = 100 kJ

Common slips

• Writing that energy is recycled through an ecosystem. Energy flows and is lost as heat; nutrients cycle.
• Drawing arrows from consumer to producer. Arrows point to the organism that eats.
• Confusing habitat (where) with community (all populations together).
• Saying decomposers make food. They break down dead matter.